The activation of CD4 T cells can lead to the generation of antigen experienced cells some of which are effector cells important in the immediate clearance of pathogens and some of which are memory cells important in the rapid elicitation of a response to pathogens encountered previously. The main goal of this proposal is to study the events leading to the generation of antigen experienced CD4 T. Once generated naive and antigen experienced cells will be analyzed for differences in their activation requirements and in the nature of the response elicited. The project will consist of 2 parts: 1) the characterization of phenotypic, functional and biochemical differences between naive, memory and effector CD4 T cells, and 2) the examination of the role of antigen presenting cell types and cytokine expression in the development of effector and memory cells from naive CD4 T cells.